1. Field of the Invention
This invention relates to a reading optical system which is used to read originals in a facsimile apparatus and which is easy to illuminate and durabile and easy to manufacture.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings is a sideways cross-sectional view showing an example of the reading optical system according to the prior art. Reference numeral 1 designates a light-guide held by transparent blocks 2 and 3, reference numeral 4 denotes a light sensor, and reference numeral 6 designates the surface of an original. The light-guide 1 has been provided in contact with the origin P of the inclined bottom surface of the block 3, and the original 6 near the P-point has been read by the light sensor 4 through the light-guide. Also, the illuminating light has been caused to enter from between the original 6 and the inclined bottom surface of the block 3.
Such a conventional reading optical system has suffered from a disadvantage that the lower end of the light-guide 1 is liable to be abraded or injured by the contact thereof with the surface 6 of the original. However, if an attempt is made to install the light-guide 1 in spaced apart relationship with the P-point, the spacing between the end surface of the light-guide 1 and the surface 6 of the original becomes greater and this leads to the occurrence of a problem that the degree of resolution of the reading is reduced. Further, if an attempt is made to make the angle of the inclined surface with respect to the surface of the original smaller so that the end surface of the light-guide 1 is not very much spaced apart from the surface 6 of the original, the incidence range of the illuminating light becomes narrower, and this leads to an inconvenience that arrangement of a light source, etc. becomes difficult. Thus, it has heretofore been very difficult to obtain a reading optical system which will satisfy the requirements of protection of the light-guide, a high degree of resolution and ease of illumination at once.